Related prior methods are based on syntactic (e.g., Boolean) search or the use of textual markup languages (e.g., XML). These methods have been incorporated into every major Web and off-line search engine. Syntactic search engines are fine if you know exactly what you are looking for and are sure that the document being searched will use the same syntax. Otherwise, appropriate textual passages will not be returned, which of course runs counter to the prima facia of search itself. Boolean queries here just serve to further constrain the returned results. Textual markup languages allow for efficient semantic search of textual documents, but there is much labor (cost) in manually marking up large corpuses and the evidence is that such markups are very likely to be error prone. Imagine, if you will, the cost and errors associated with any attempt to manually markup the entire Library of Congress as a point of contention.